In recent years, many countries have devoted great efforts to developing clean energy alternatives in order to solve the problems of atmospheric environmental pollution and global warming. In particular, marine salinity gradient power generation recently has received much attention.
At the same time, the development of large-capacity electric power storage technology capable of storing electric energy generated by various alternative energies has been raised as a key point in the foundation of the green industry of the future. Most such future technologies for power storage are based on the principles of ion absorption (charge) and desorption (discharge) such as Li-ion batteries or super capacitors, and therefore, countries over the world are proceeding with major research and development efforts to accomplish high-efficiency densification and capacity extension by improving the charge-discharge characteristics of materials and parts.
Meanwhile, such principles have also recently been employed in water treatment applications including treatment of purified water or waste water, and sea water desalination, etc., whereby water is treated with an energy cost which is very decreased compared to the existing methods of evaporation or reverse-osmosis (RO); that is, a capacitive deionization (CDI) process is now under development.
For a power storage and water treatment system using the identical principles as described above, the most significant problem is the high cost of equipment as well as reduction of efficiency in the extension of capacity. In other words, due to an increase in the surface area of electrodes for upscaling, and irregularities in the electrical field distribution of the electrode, limited amounts of active materials in thin film electrodes coated on current collectors, a decrease in the contact area between the active material and electrolyte by binders during coating, decrease in charge-discharge efficiency, and so forth, the number of unit cells must be stacked, thereby causing high equipment costs, and specifically, a capacitive deionization (CDI) process encounters the problem of increasing operational costs due to the loss of water (electrolyte) pressure in the stack flow.
In order to solve the above problem, the present applicant has developed a capacitive flow-electrode device (Korean Patent No. 10-1233295), and used the same for development (Korean Patent No. 10-1318331), energy storage (Korean Patent No. 10-1210525), and water treatment (Korean Patent No. 10-1221562).
Although it is possible to supply electrodes having an infinite electrode capacity to unit cells by the flow-electrode proposed in the inventions above, existing technologies such as apparatuses including a redox flow battery, etc., which use the flow-electrode, are required to increase electrode area or to be stacked to provide a large capacity. However, in existing technologies, constitutional unit elements including positive and negative electrode collectors are infinitely stacked.
As a result, the stacking of the unit cells not only cause a greatly increased volume, but also has a problem in that the number of components increases due to a variety of flow channels, thereby increasing the costs of manufacturing an apparatus.